Fracture Mechanics Of Composite Materials Research Articles

Methodology of residual strength prediction of composite structures with low-velocity impact damage based on NDT inspections and numerical-experimental CAI testing

One of the most challenging tasks is to evaluate a structural condition and predict a residual strength when damage is present in a composite structure. Such a prediction is usually performed based on experimental destructive testing on specimens, which often does not reflect the geometrical complexity of a component with damage, or based on numerical simulations, which are difficult to parametrize due to the complexity of fracture mechanisms of composite materials. In this paper, we proposed a hybrid methodology based on evaluation of results of the ultrasonic non-destructive testing technique supported with numerical modeling and compression after impact (CAI) tests to evaluate residual strength of glass- and carbon-reinforced polymer composite structures. Based on ultrasonic C-scans processing and incorporation of impact damage shapes in numerical models and further evaluation of the obtained results in the light of CAI tests, the model for the prediction of residual strength in composites was developed.

Investigation of Failure Mechanisms in Ceramic Composites as Potential Railway Brake Disc Materials.

Ceramic composite materials have been efficiently used for high-temperature structural applications with improved toughness by complementing the shortcomings of monolithic ceramics. In this study, the fracture characteristics and fracture mechanisms of ceramic composite materials were studied. The ceramic composite material used in this study is Nicalon ceramic fiber reinforced ceramic matrix composites. The tensile failure behavior of two types of ceramic composites with different microstructures, namely, plain-weave and cross-ply composites, was studied. Tensile tests were performed on two types of ceramic composite material specimens. Microstructure analysis using SEM was performed to find out the relationship between tensile fracture characteristics and microstructure. It was found that there was a difference in the fracture mechanism according to the characteristics of each microstructure. In this study, the results of tensile tests, failure modes, failure characteristics, and failure mechanisms were analyzed in detail for two fabric structures, namely, plain-weave and cross-ply structures, which are representative of ceramic matrix composites. In order to help understanding of the fracture process and mechanism, the fracture initiation, crack propagation, and fracture mechanism of each composite material are schematically expressed in a two-dimensional figure. Through these results, it is intended to provide useful information for the design of ceramic composite materials based on the mechanistic understanding of the fracture process of ceramic composite materials.

A Crashworthy Problem on Composite Structures Using a Mathematical Approach

Abstract During the last decades the attention given to vehicle crash energy management has been centred on composite structures. The use of fibre-reinforced plastic composite materials in automotive structures, in fact, may result in many potential economic and functional benefits due to their improved properties respect to metal ones, ranging from weight reduction to increased strength and durability features. Although significant experimental work on the collapse of fibre-reinforced composite shells has been carried out, studies on the theoretical modelling of the crushing process are quite limited since the complex and brittle fracture mechanisms of composite materials. Moreover most of the studies have been directed towards the axial crush analysis, because it represents more or less the most efficient design. A mathematical approach on the failure mechanisms, pertaining to the stable mode of collapse of thin-walled composite structures subjected to axial loading, is investigated. The analysis is conducted from an energetic point of view. The main energy contributions to the absorption (bending, petal formation, circumferential delamination, friction) are identifies and then the total internal energy is equated to the work done by the external load. The total crushing process can be seen as a succession of deformation states, each responsible for a partial absorption. The minimum configuration for each impact force in the specific state of deformation, function of several variables and dependent on geometric and material parameters is obtained. A comparison between theory and experiments concerning crushing loads and total displacements is presented, showing how the proposed analytical model is effective in predicting the energy absorption capability of axially collapsing composite shells.

Investigations of the Fracture Mechanism of Carbon/Epoxy Composites by AE Signal Analyses

Although the AE method provides useful information on the operating fracture processes of materials, a synthesized evaluation of AE signals using several AE parameters is necessary for composite materials because AE signals arise from various fracture processes. In this paper, the relationships between several AE paramaters and AE original sources were investigated, and fracture mechanisms of CFRP are discussed in terms of observations of fracture surfaces and internal damage of the laminates by a SEM and a scanning acoustic microscope (SAM), respectively. Synthesized AE signal wave analyses including the distributions of AE amplitude, AE event duration, and counts/duration (corresponding to frequency), give us useful and powerful information to analyze the complicated fracture mechanisms of composite materials. The fracture in tensile tests and cyclic tensile tests of unidirectionally reinforced carbon/epoxy composites goes through fiber/matrix interface debond and fiber breaking.

Japanese Aerospace Literature This month: Fracture Mechanics of Composite Materials (July 1990)

Japanese Aerospace Literature This month: Fracture Mechanics of Composite Materials (July 1990)

Soviet Aerospace Literature This month: Fracture Mechanics of Composite Materials (July 1990)

Soviet Aerospace Literature This month: Fracture Mechanics of Composite Materials (July 1990)

Investigations of the fracture mechanism of carbon/epoxy composites by AE signal analyses.

Although the AE method provides useful information on the operating fracture processes of materials, a synthesized evaluation of AE signals using several AE parameters is necessary for composite materials because AE signals arise from various fracture processes. In this paper, the relationships between several AE paramaters and AE original sources were investigated, and fracture mechanisms of CFRP are discussed in terms of observations of fracture surfaces and internal damage of the laminates by a SEM and a scanning acoustic microscope (SAM), respectively. Synthesized AE signal wave analyses including the distributions of AE amplitude, AE event duration, and counts/duration (corresponding to frequency), give us useful and powerful information to analyze the complicated fracture mechanisms of composite materials. The fracture in tensile tests and cyclic tensile tests of unidirectionally reinforced carbon/epoxy composites goes through fiber/matrix interface debond and fiber breaking.

Diffraction of acoustic waves by two nonparallel circular cylinders

i. A. Ya Gol'dman, N. F. Savel'eva, and V. I. Smirnov, "Study of the mechanical properties of cloth glass-plastics in tension and compression normal to the reinforcement plane," Mekh. Polim., No. 5, 803-809 (1968). 2. O. M. Guz', Dopov, Akad. Nauk UkrRSR, Ser. A, No. 3, 236-238 (1969). 3. A. N. Guz', "Fracture mechanics of composite materials in axial compression (brittle fracture)," Prikl. Mekh., 18, No. i0, 3-16 (1982). 4. A. N. Guz', "Continuum theory of fracture in the compression of composites with an elastoplastic matrix," Dokl. Akad. Nauk SSSR, 262, Nd. 3, 556-560 (1982). 5. A. N. Guz', "Continuum theory of the fracture of composites in compression in the case of a complex stress state," Prikl. Mekh., 22, No. 4, 3-19 (1986). 6. A. N. Guz', A. A. Kritsuk, and R. A. Emel'yanov, "Character of fracture of a unidirectional glass-plastic in compression," Prikl. Mekh., ~, No. 9, 118-131 (1969). 7. A. N. Guz', M. A. Cherevko, G. G. Margolin, and I. M. Romashko, "Fracture of unidirectional boron-aluminum composites in compression," Mekh. Kompozit. Mater., No. 2, 226-230 (1986). 8. G. S. Kats and D. V. Milevski (eds.), Fillers for Polymer Composites, Handbook [Russian translation], Khimiya, Moscow (1981). 9. B. U. Rosen, "Mechanics of the strain-hardening of composites," in: Fiber Composites [Russian translation], Mir, Moscow (1967), pp. 54-96. 10. B. U. Rosen and N. F. Dow "Fracture mechanics of composites," in: Fracture [Russian translation], Vol. 7, Pt. i. Fracture of Nonmetals and Composite Materials. Inorganic Materials (glasses, rocks, composites, ceramics, ice), Mir, Moscow (1976), pp. 300-366. ii. N. F. Dow and I. J. Grunfest, "Determination of most needed potentially possible improvements in materials for ballistic and space vehicles," General Electric Company, Space Sci. Lab. TISR 60 SD 389, June, 1960.

Studies on fracture mechanisms of CFRP by acoustic emission method.

Carbon fiber reinforced plastics (CFRP), which is one of the advanced composites, have excellent properties of specific strength and rigidity. They have been used for lightening the mass of machines and the structures. It is thought that the fracture mechanisms of composite materials are so complicated that an investigation is necessary to make clear the fracture behaviors and mechanisms of the materials. Therefore, by using the results of frequency analysis of the acoustic emission of the model CFRP in the previous paper, it is found, in this paper, that the acoustic emission which is produced by the deformation and the fracture of unidirectional composite laminates and three directional ones are classified by the frequency, and that the fracture mechanisms of these composite materials can be clarified.

筑波研究学園都市における精密技術展望 ＩＩ 複合材料の破壊力学特性

筑波研究学園都市における精密技術展望 ＩＩ 複合材料の破壊力学特性

Fracture mechanics of composite materials

The above circumstances lead to models based on a discussion of the structure of a composite being used most frequently in the fracture mechanics of composite materials. In view of the stochastic properties of the elements in the structure, especially the dispersion in the strength of the fibers, stochastic fracture models are widely used [4-7]. Nevertheless, there has been no success so far in suggesting models which predict the strength of a composite and the dimensions of the permissible defects. Furthermore, there has been no success in reconciling the proposed models qualitatively with the results of tests on specimens containing cracks or notches. The purpose of this study is to fill this gap partially. In this paper semideterministi c models are developed, distinguished by being based on probability considerations, butthe final results are presented in deterministic form. These results are related to the average or most probable values of the macroscopically measurable quantities, which can be compared with the average data from experiments. The most appreciable difference in the proposed approach is that a crack in a composite is considered as a formation which, owing to delamination, has extension in the direction of reinforcement, its dimension in this direction entering explicitly or implicitly into all the principal relationships. The proposed equations have a qualitative approximate nature. As is frequently done, we shall carry out the operations at the physical level of rigor [8]. In particular, we shall omit factors on the order of unity (except for cases where these factors are necessary for qualitative conclusions) and discard small terms. For macroscopic quantities we shall give "almost certain ~ estimates, Le., with a probability on the order of unity, and we shall identify the deterministic quantities with distribution medians, with quantilers on the order of 1 - e -1 = 0.632.. , etc.

The mechanical properties of filamentary niobium tin composites

The mechanical properties of filamentary Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn superconducting composites have been investigated. The effect of reaction conditions and variation of component dimensions on the strain which can be accommodated before loss of current carrying capacity occurs has been determined, Critical strains to failure lie within the range 1-3%. The failure mechanism of Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn layers is discussed in terms of the fracture mechanics of composite materials. Commercial types of composite consisting, typically, of 1500 filaments in bronze were found to withstand repeated stressing to 3.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> Nm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> in liquid helium without degradation of superconductivity.